1. Field of the Invention
The present invention relates to a network termination device, an alarm transfer system and an alarm transferring method for use in a system for transmitting an Ethernet signal encapsulated by the generic framing procedure (the xe2x80x9cGFPxe2x80x9d) or the like. More specifically, this invention relates to a network termination device, an alarm transfer system and an alarm transferring method, which are collectively designed for a case when a link down of one Ethernet termination device is detected so as to inform a link down alarm to an opponent Ethernet termination device and thereby to disconnect a link with an opponent terminal.
2. Description of the Related Art
In the case where the Ethernet is used for communication between computers (more specifically, personal computers), network monitoring across-the-board as the Internet has not been conventionally conducted. It is due to the fact that the Internet has been offered originally as a best-effort service (which refers to a service usable depending on bandwidth margins, however, such bandwidths or quality are not always guaranteed).
Nevertheless, there are growing movements for utilizing the Internet as a backbone network, and needs for guarantee of the bandwidth and the quality are increasing. For example, a protection function for relieving lines by switching to a backup transmission path upon failures of a main transmission path is required as guarantee of quality.
FIG. 1 shows a sequence of a conventional alarm transferring operation.
Conventional monitoring has been highlighted on whether a data link is established between one terminal and another terminal. In this case, a failure can be detected as disconnection of a link with the opponent terminal regardless of where such a failure happens between the terminals. Further, control for disconnecting the sender""s terminal is carried out, whereby the sender""s terminal can recognize the failure by itself as disconnection to the link.
The above-described operation does not change if a transponder is interposed between the terminals, as long as the transponder transfers data from the terminal intactly without processing.
For example, when a plurality of Ethernet signals are multiplexed and then transferred, it is necessary to identify as to which Ethernet signal each packet is originally contained. Therefore, a method of encapsulating a packet on an intermediate zone by use of the GFP or the like while posting an identification code in a GFP header is conceivable.
However, upon transfer of data encapsulated by use of the GFP technology or the like, data link control between terminals is disabled. As a result, the opponent terminal cannot detect a failure occurred somewhere on the intermediate zone.
An object of this invention is to provide a mode of alarm transfer for use in a case of transferring data encapsulated by the GFP or the like on an intermediate zone of an Ethernet path.
A network termination device of this invention is a network termination device for transmitting a data signal from a terminal connected through a link toward another network termination device via a transmission path. Here, the network termination device includes an alarm processing circuit for detecting notification of a link down of the link connected to the other network termination device and occurrence of a failure on the transmission path. Moreover, the network termination device disconnects the link forcibly and withholds notification of the disconnection outward when the alarm processing circuit detects any of the notification and the occurrence of the failure.
An alarm transfer system of this invention includes a plurality of network termination devices severally connected to corresponding terminals, the network termination devices being connected to one another via a transmission path, in which at least one of the network termination devices includes the above-described network termination device.
An alarm transferring method of this invention is used in a system for transmitting a data signal between a first network termination device connected to a first terminal through a first link and a second network termination device connected to a second terminal through a second link via a transmission path. Here, the method includes the steps of detecting notification from the second network termination device concerning a link down of the second link and occurrence of a failure on the transmission path by use of the first network termination device, and disconnecting the first link forcibly based on the detection. Here, when the step of disconnecting is executed, the first network termination device withholds notification of the disconnection of the first link to the second network termination device.
Another alarm transferring method of this invention of another configuration is used in a system for transmitting a data signal among at least three network termination devices via a transmission path, the network termination devices being severally connected to corresponding terminals through links. Here, the method includes the steps of detecting notification concerning a link down of the link from any other network termination device and occurrence of a failure on the transmission path connected to the network termination device performing detection by use of any one of the network termination devices, and performing forcible link down control based on the detection. Here, the network terminal device withholds notification of execution of the link down control to the rest of the network termination devices.